Selenium is 1 of maybe 2 nutrients where the amount in your food depends on the soil. It depends on where the food grew rather than on the food itself.
That is why 2 identical diets in 2 different countries can differ several-fold.
Quick Answer: Where Does Selenium Come From?
Brazil nuts are by far the richest source, followed by seafood, organ meats, eggs and cereals. The amount in any plant food depends on the selenium content of the soil where it grew, which varies enormously by region. That is why deficiency is common in some parts of the world and essentially absent in others, and why 1 Brazil nut is not a reliable dose against the 55 mcg recommended intake.
Key Takeaways
- Brazil nuts are the 1 richest food source by a wide margin.
- Soil content decides how much selenium any 1 plant food carries.
- 2 identical diets in 2 different regions can differ several-fold.
- Seafood, organ meats and eggs are the other 3 main food sources.
- The adult RDA is 55 mcg, which most Western diets already supply.
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Why Soil Decides Everything
This is the fact that makes selenium different from almost every other nutrient on the shelf.
- Plants take up: Whatever selenium the soil holds.
- Animals concentrate: What they ate, so meat follows the same map.
- Result: Regional differences of several-fold in ordinary diets.
- Consequence: Deficiency is geographic rather than dietary.
What the mineral does once you have it is in the mineral explained.
The Food Sources, Ranked
These are the practical sources, with the caveat that every number is soil-dependent.
| Food | Note |
|---|---|
| Brazil nuts | By far the richest, and the most variable |
| Tuna and sardines | Consistently high among seafood |
| Organ meats | Liver and kidney in particular |
| Eggs | Modest but reliable |
| Wheat and cereals | Entirely dependent on where they were grown |
Brazil nuts are the reason this article exists. Their content varies so widely that the same number of nuts can supply the RDA or approach the upper limit.[2]Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT) — JAMA (2009) View source
Who Actually Becomes Deficient
Deficiency is real but it is not evenly distributed, and knowing the pattern is more useful than a symptom list.
- Geography: Regions with low-selenium soil, historically parts of China.
- Medical: Long-term parenteral nutrition without supplementation.
- Gut conditions: Where absorption is impaired.
- Not usually: Someone eating a varied Western diet.
Most people reading this in the United States are not deficient, which reframes the question from correcting a shortfall to deciding whether extra helps.
Whether Extra Helps
That is the question the big trials tried to answer, and the answer was not encouraging.
- Cancer prevention: Tested directly and not demonstrated.
- Thyroid autoimmunity: Contested, with reviews disagreeing.
- Cardiovascular outcomes: Examined in broad micronutrient reviews.
- The pattern: Correcting a deficiency differs from adding to sufficiency.
A 2022 review in the Journal of the American College of Cardiology systematically quantified micronutrient effects on cardiovascular outcomes across randomized trials.[3]Micronutrient Supplementation to Reduce Cardiovascular Risk — Journal of the American College of Cardiology (2022) View source The prevention question specifically is in what the big trial found.
The Brazil Nut Problem
It deserves its own section because it is the single most common way people get this wrong.
- The advice you see: Eat 1 or 2 Brazil nuts a day.
- The problem: Content varies by an order of magnitude with soil.
- The consequence: The same 2 nuts can be 50 mcg or several hundred.
- The safer approach: Treat them as an unmeasured dose, not a snack.
Trials had to control the amount precisely, which is exactly what a handful of nuts cannot do.[4]Selenium Supplementation in Patients with Hashimoto Thyroiditis: A Systematic Review and Meta-Analysis of Randomized Controlled Trials — Thyroid (2024) View source
A capsule is not better than food in any nutritional sense. It is simply the only version of this mineral that comes with a number on it. The ceiling is in the upper limit explained.
How to Decide
Three questions cover it, and none of them requires a blood test to start.
- Do you eat Brazil nuts regularly? Then probably not.
- Does your multivitamin contain selenium? Then count that first.
- Do you have a specific reason? Thyroid autoimmunity is the common 1.
- Otherwise: A varied diet in most regions already supplies 55 mcg.
If you decide a measured amount is what you want, the version with a number on it.
Speak to a Clinician Before Supplementing Selenium If
- You already eat Brazil nuts most days, which alone can exceed the upper limit
- You take more than 1 supplement containing selenium, including a multivitamin
- You have hair loss, brittle nails or a garlic-like breath odour while supplementing
- You have thyroid disease and are considering selenium alongside levothyroxine
- You are pregnant, where the upper limit matters more and the margin is smaller
Frequently Asked Questions
What foods are high in selenium? +
Brazil nuts by a wide margin, then seafood, organ meats and eggs. All 4 vary with the soil behind them.
How many Brazil nuts equal 200 mcg? +
There is no fixed answer, because content varies by an order of magnitude. 2 nuts can be 50 mcg or several hundred.
Am I likely to be selenium deficient? +
In most Western diets, no. Deficiency is largely geographic, tied to the 1 factor of low-selenium soil.
What are the symptoms of selenium deficiency? +
It is rare enough in the West that symptoms are not a useful screening tool. Geography and gut conditions are the 2 better clues.
Do vegetarians need more selenium? +
Plant sources depend entirely on soil, so it varies by region rather than by diet type alone. Brazil nuts are 1 easy plant source.
Is food selenium better than a supplement? +
Not nutritionally, but food is unmeasured. A capsule is the 1 version of this mineral that carries a number.
Does cooking destroy selenium? +
It is 1 mineral, so it is not destroyed by heat the way some vitamins are. Losses are minimal in normal cooking.
Should I get my selenium level tested? +
It is available but rarely necessary in a varied Western diet. Discuss it if you have 1 of the specific risk factors.
Can you get too much selenium from food? +
Yes, and Brazil nuts are the usual route. That is 1 reason to treat them as a dose rather than a snack.
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